Inductions heating coil



March 17, 1964 v E. F.. MQBRIEN ETAL 3,125,655

INDUCTIONS HEATING con FiledMay 15, 1960 INVENTORS Edward F. McBrien 8\ Richard A.Sommer.

ATTORNEY United States Patent 3,125,655 INDUCTION HEATING COIL Edward F. McBrien and Richard A. Summer, Parma, Ohio, assignors to The Ohio Crankshaft Company, Cleveland, Ohio Filed May 13, 1960, Ser. No. 29,015

Claims. (Cl. 219-1049) This invention relates to induction heating coils and more particularly to an induction heating coil having a minimized internal diameter to accommodate workpieces of very small cross sectional areas.

As is well known, it is highly desirable in the design of induction heating equipment to provide a coil with an inside diameter as small as possible, the obvious reason being that in order to obtain eflicient magnetic coupling between the coil and a workpiece positioned therein the clearance bteween the coil and the part to be heated should be reduced to a minimum. The usual induction heating coil is formed from a tube of electrically conductive material whereby a cooling fluid may flow through the hollow tube, and in most cases the inside diameter of the coil is determined by the required clearance between the coil and the part which is to be heated. In the case of workpieces of very small cross section, however, the internal diameter is limited by the size of the tubing from which the coil is to be formed. That is, there is a minimum radius of curvature which can be achieved in a hollow metal tube of the proper size with the result that in the case of very small workpieces, the clearance between the coil and the part to be heated is much greater than that desired. It may, of course, be possible to employ small [diameter tubing to obtain .a coil of reduced cross section; however, the narrow passageway through such tubing restricts the flow of cooling liquid and necessitates the use of high pressures.

A primary object of the present invention is to provide an induction heating coil having a minimized internal diameter to accommodate workpieces of very small cross sectional areas.

Another object of the invention is to provide an induction heating coil formed from a thin strip of electrically conductive material wound in a helical configuration whereby a very small radius of curvature may be produced in the strip.

A :funther object of the invention resides in the provision of means [for cooling a small diameter heating coil of the type described above without the necessity tor high pressures on the cooling fluid.

Still another object of the invention is to provide a r new and improved induction coil adapted to heat thin magnetic strip and the like where low power densities and extremely large coils are required.

'In accordance with the invention, an induction coil is I,

provided comprising a solid strip of electrically conductive material wound about an axis to form an elongated helix in which the short transverse dimension of the strip is substantially perpendicular to the axis of the helix. In this manner, a very small radius of curvature can be produced in the strip to form circular coils of extremely small internal diameter, or rectangular coils of particularly narrow cross section. Since the strip does not have a cooling passage extending therethrough as in conventional coils, an external cooling tube in the tEorm of a helix is provided with successive turns being tastened at one point to successive turns of the strip helix. This cooling tube has a much larger diameter than the diameter of the helix defined by the heating coil whereby the resistance to fluid flow through the tube is minimized. Also the impedance of each turn of the cooling tube helix is much larger than the impedance oi the strip helix so that a minimum of currents flow in the cooling tube helix.

3,125,655 Patented Mar. 17, 1964 "ice The foregoing and other objects and features of the invention will become apparent from the following detalied description taken in connection with the accompanying drawings which form a part of this specification in which:

FIGURE 1 is an elevational view of one embodiment of the invention particularly adapted for use in heating long slender workpieces such as rods or wire;

FIGURE 2 is a cross sectional view taken along line IIII of FIGURE 1; and

FIGURE 3 is a perspective view of another embodiment of the invention particularly adapted for use in heating thin strip material and the like.

Referring to FlGURES 1 and 2, the embodiment of the invention shown comprises a heating coil 10 formed of a plurality of turns of an elongated ribbon of electrically conductive material, such as copper, which is wound about an axis to form a helix in which the long transverse dimension of the ribbon extends substantially perpendicular to the axis of the helix. At the same time, the edges of the ribbon in each turn of the coil face each other. As will be understood, a strip of this sort is relatively flexible; and, consequently a very small radius of curvature can be produced in a strip to achieve an induction coil having a very small internal diameter. Thus, the clearance between the inner periphery of the coil and a workpiece, such as rod 12, can be maintained at a minimum to effect good magnetic coupling.

Surrounding the induction coil id, and secured thereto at spaced points along its length, is a cooling coil 14 which, as shown in FIGURE 2, has a much larger diameter than the diameter of the coil 10. As shown in FIG- URE 1, the cooling coil 14 is formed of a plurality of turns of copper tubing with each turn brazed or otherwise securely hastened to the coil 10 at one point 1 1 on each turn of the coil. However, the coil 14 may be secured to coil it) at as many points as desired by varying the pitch of the helix from which it is formed. Furthermore, two or more cooling tubes may be used if they are assembled similar to a double threaded screw along the length of the coil. With this arrangement, it can be seen that an extremely small diameter heating coil can be achieved while, at the same time, a cooling tube of relatively large diameter can be employed to reduce resistance to the flow of fluid through the coil to a minimum.

Although the heating coil It) is shown in FIGURE 1 as being circular, it may be rectangular, hexagonal or any other configuration and may be made irom a strip of any thickness, including foil or even copper plating. An embodiment of the invention having a rectangular cross section is shown in FIGURE 3 and is adapted for use in installations where thin strip material must be heated. Such heating applications require extremely wide coils and low power densities; and thus, the coil can best be made from copper strip to which cooling tubes are brazed.

In FIGURE 3 the coil 16 is again formed from a thin strip of electrically conductive material. In this case, however, it defines a cavity having a long narrow cross section for the reception of a wide, thin strip 18 which is to be heated. A cooling tube 20 again surrounds the coil '16 and is brazed at 21 along the entirety of one side of each turn of the coil along its long transverse dimension, with the coil being looped through a wide arc on the other side of the coil for each turn as at 22. As will be understood, this configuration facilitates much better heat transfer than in the case of FIGURES 1 and 2 wherein the cooling tube makes point contact only with each turn of the coil. At the same time, the relatively large radius of curvature in the coil presents a minimum amount of resistance to the flow of fluid the-rethrough.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled inthe art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

Having thus described our invention, we claim:

1. An induction coil comprising a ribbon of solid electrically conductive strip material wound about an axis to form an elongated helix having a minimized internal dimension and in which the long transverse dimension of the ribbon extends substantially [perpendicular to said axis and in which the edges ot successive turns of the helix face each other, and an elongated helical cooling tube surrounding the helical ribbon and secured thereto as spaced points along the length of said ribbon, the diameter of the helix defined by said cooling tube being substantially greater than the diameter ot the helix defined by said ribbon whereby the helical ribbon is spaced from said cooling tube helix at the area between said spaced points and the resistance to the flow of fluid through the cooling coil will be minimized.

2. An induction coil comprising a ribbon of solid electrically conductive strip material Iwound about an axis to form an elongated helix having a minimized internal dimension and in which the long transverse dimension of the ribbon extends substantially perpendicular to said axis and in which the edges of successive turns of the helix face each other, and a cooling tube secured to the helical ribbon at spaced points along the length of said ribbon, said cooling tube being wound in a helix having a diameter larger than the diameter of the helix defined by the electrically conductive ribbon and having its inner periphery secured to the outer periphery of the helical ribbon whereby the axis of the helix defined by the cooling tube will be offset with respect to that of the helix defined by said ribbon.

3. The combination claimed in claim 2 wherein each turn of the helical cooling tube is secured to a corresponding turn in the helical ribbon whereby the heat generated in the ribbon may be transferred to the cooling tube.

4. An induction coil for heating articles having small cross-sectional dimensions comprising a ribbon of solid electrically conductive strip material wound about an axis to form a helix having a minimized internal dimension, said internal dimension being slightly larger than the cross-sectional dimension of said article and a cooling tube secured to the helical ribbon at spaced points along the length of said ribbon, said cooling tube formed into a helix having an axis and said cooling tube helix having an internal dimension substantially larger than the external dimension of said helical ribbon whereby the helical axis of said ribbon is substantially olfset from the helical axis oct said cooling tube.

5. An inductor comprising an induction heating coil and a cooling unit, said heating coil being formed into a first helix from a strip of solid electrically conductive material, said first helix having a minimized internal dimension and an external dimension determined by the thickness of said strip material, said cooling unit being formed into a second helix from a tubular material, said second helix having an internal dimension substantially larger than the external dimension of said first helix, said first and said second helix connected at spaced points along a contact line between the internal surface of said second helix and the external surface of said first helix Whereby the first and second helixes are substantially spaced at the surface area opposite said contact line on each I helix.

References Cited in the file of this patent UNITED STATES PATENTS 1,789,229 Gebhard Jan. 13, 1931 2,481,071 Bowlus Sept. 6, 1949 2,568,169 Raczynski Sept. 18, 1951 2,897,328 Alf et al. July 28, 1959 FOREIGN PATENTS 1,067,146 Germany Oct. 15, 1959 

1. AN INDUCTIONCOIL COMPRISING A RIBBON OF SOLID ELECTRICALLY CONDUCTIVE STRIP MATERIAL WOUND ABOUT AN AXIS TO FORM AN ELONGATED HELIX HAVING A MINIMIZED INTERNAL DIMENSION AND IN WHICH THE LONG TRANSVERSE DIMENSION OF THE RIBBON EXTENDS SUBSTANTIALLY PERPENDICULAR TO SAID AXIS AND IN WHICH THE EDGES OF SUCCESSIVE TURNS OF THE HELIX FACE EACH OTHER, AND AN ELONGATED HELICAL COOLING TUBE SURROUNDING THE HELICAL RIBBON AND SECURED THERETO 